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Abstract

Conventional imaging systems rely upon illumination light that is scattered or transmitted by the object and subsequently imaged. Ghost-imaging systems based on parametric down-conversion use twin beams of position-correlated signal and idler photons. One beam illuminates an object while the image information is recovered from a second beam that has never interacted with the object. In this Letter, we report on a camera-based ghost imaging system where the correlated photons have significantly different wavelengths. Infrared photons at 1550 nm wavelength illuminate the object and are detected by an InGaAs/InP single-photon avalanche diode. The image data are recorded from the coincidently detected, position-correlated, visible photons at a wavelength of 460 nm using a highly efficient, low-noise, photon-counting camera. The efficient transfer of the image information from infrared illumination to visible detection wavelengths and the ability to count single photons allows the acquisition of an image while illuminating the object with an optical power density of only 100pJcm−2s−1. This wavelength-transforming ghost-imaging technique has potential for the imaging of light-sensitive specimens or where covert operation is desired.

Figures (3)

Fig. 1. Experimental setup. The nondegenerate SPDC process generates a visible/infrared photon pair at the BBO crystal, and these photons are split at a dichroic mirror. The infrared photon probes an object and the transmitted photons are detected by a single-element heralding detector (InGaAs/InP single-photon avalanche diode). This detection event triggers the intensifier of the ICCD camera, which detects the delayed yet spatially correlated visible photon. The recovered image of the object is the accumulation of many visible photon detections by the ICCD.

Fig. 2. Image of a test object. A stencil of the letter “IR” obtained in visible light by an ICCD camera, even though the object was illuminated only by infrared radiation. The object is etched into gold deposited onto a 387 μm thick silicon substrate. For every infrared photon that probed the object and was detected by the heralding detector, the ICCD camera was triggered to record the position-correlated visible photon. The images were formed by summing over many photon-detection events as labeled.